Flash Flooding and Flooding in Alaska, July 27 to 31, 2003

Record rainfall occurred over the central interior of Alaska in late July bringing rivers and streams above their banks. Rainfall amounts of one to three inches fell in the Denali area. The heaviest rain fell across the Fairbanks North Star Borough, where totals ranged from 3 to 6 inches from the 26th through the 28th. During a 24-hour period from July 26 to 27th, Fairbanks received 2.56 inches of rain, equaling 25% of the average annual precipitation. The July monthly total for Rain at Fairbanks was 5.96 inches, a new July record and 4th highest among all months on record. Damage amounts include $81,000 in repairs reported by the State of Alaska are an estimateAll this rain resulted in some of the highest water levels seen on the Chena and Chatanika Rivers since the disastrous flood of 1967. The high volume of water coming down the Chena River resulted in the lowering of the flood gates at the Chena Flood Control Project by the US Army Corps of Engineers Tuesday morning the 29th. Water levels on the Chena River dropped enough by Thursday the 31st to allow the Corps to raise the gates and let the river flow unrestricted. Without the flood project in place, much of the low-lying areas around Fairbanks would have likely flooded. The meteorological conditions resulting in this rainfall were very different from the 1967 flooding. In August 1967, strong southwest flow over the state pushed a substantial amount of subtropical air from the Pacific Ocean into Alaska. Ex-typhoon Hope got picked up in this flow and supplied more moisture, while a stationary frontal boundary over the central interior allowed rainfall to persist for nearly a week. Above average snowfall the previous winter, along with above average summer precipitation preceded the August 1967 flooding.The flooding of late July 2003 was preceded by a below average winter snow pack and summer precipitation. in the middle of July, a strong upper level Low Pressure center over the Arctic Ocean dropped south over Alaska, resulting in vigorous northwest flow at upper levels over northern Alaska. Although usually a dry flow pattern, the northwest flow picked up moisture from the largely ice-free Chukchi Sea and moisture was also enhanced due to a tropical system that had moved into China the previous week. The moisture from this tropical system made its way to the Russian Arctic where it was picked up in the northwest flow. During the height of the event, a jet stream at upper levels approaching 140 mph was moving across the southern interior of Alaska. This is when the heaviest rain fell in the Fairbanks area, during the 12 hours from midnight Saturday July 26 to noon Sunday July 27. The topography of the Chena basin provided additional lift of this moist airmass in the Fairbanks area...and as in 1967, a frontal boundary stalled over the central interior. Flash flooding occurred at:Zone 221 - Elliott Highway Mile 57 was closed due to the Tolovana River flooding, as reported by the State of Alaska Department of Transportation.Zone 222 - Streams draining into the Chatanika River were flooding in the areas near mile 40 of the Steese highway. Several road washouts occurred on the Stese Highway. At least one road in the hills just north of Fairbanks had water flowing over it from an overbank stream.Zone 225 - Some rock slides along the Parks Highway; Carlo Creek south of Denali Park overflowed its banks on early on the 28th and flooded cabins, roadways, and businesses, as well as eroding sections of the Parks Highway. The River flooding occurred at:Zone 221: Minor flooding occurred at Nenana. Zone 222: Several houses and cabins along the Chatanika River were flooded, as well as some cabins on the upper Chena River. Several feet of water covered Mile 37.2 Chena Hot Springs Road and this forced the Alaska Department of Transportation close the road late on the 27th. The swift moving water ripped up pavement and covered the road with trees and debris. A few houses, roads, and yards adjacent to the Little Chena River were also flooded. Flood waters crested on the Chatanika River at the Steese Highway bridge and on the upper Chena River at the Mile 40 bridge on Monday the 28th, and on the Little Chena River on the 29th. Some groundwater and minor overbank flooding occurred at Steamboat Landing in North Pole. Minor flooding occurred in the urban sections of Fairbanks. Damage amounts include $81,000 reported by State of Alaska Division of Parks and Recreation to repair various campground and access road damages, estimated $150,000 for repair of flooded properties on the Chatanika and Little Chena Rivers, and from groundwater flooding in the Steamboat Landing subdivision, with the remainder estimated for repair of roads and highways in the area; These estimates are only guesses and could be higher.Zone 223: Minor flooding occurred on the Salcha River at the Richardson Highway Bridge as the river level just reached flood stage. The boat launch/campground just off the highway received minor flooding.